1. Field of the Invention
The present invention relates to a common voltage adjustment circuit, and in particular to a common voltage adjustment circuit employed in a liquid crystal display panel.
2. Description of the Related Art
FIG. 1 shows a schematic diagram of a conventional thin film transistor liquid crystal display (TFT-LCD) panel. As shown in FIG. 1, the TFT-LCD panel comprises a display array 1, a data driver 2, and a scan driver 3. The display array 1 is formed by interlaced data lines D11 to D1y and scan lines G11 to G1x. The interlaced data line and scan line correspond to one display unit, for example, interlaced data line G11 and scan line D11 display unit 100. Like any other display unit, the equivalent circuit of the display unit 100 comprises a thin film transistor (TFT) 10, a storage capacitor Cs10, and a liquid capacitor Clc10. One terminal of the liquid capacitor Clc10 is coupled to a common electrode providing a common voltage VCOM.
Typically, video signals transmitted by the data lines D11 to D1y are positive or negative sorted by relationship with the common voltage VCOM. Referring to FIG. 2, the common voltage VCOM comprises a direct current (DC) voltage Vcdc and an alternating current (AC) voltage Vcac. When the voltages Vcdc and Vcac are inappropriate, inaccurate display results.
FIG. 3 is an adjustment circuit 30 of a conventional TFT-LCD panel. Level of a DC voltage Vcdc is varied by adjusting a variable resistor 301, and an amplitude of an alternating current voltage Vcac is varied by adjusting a variable resistor 302, thereby modifying the common voltage VCOM to an appropriate value. Because the conventional adjustment circuit 30 is disposed outside the TFT-LCD panel, the volume of the printed circuit board and the cost both increase. Also, resistors 301 and 302 must be adjusted manually, further increasing time spent and cost.